In high frequency electron discharge devices such as cathode ray tubes, the capacitance between the control grid and the accelerating grid of an electron gun must present a small area to the other electrodes in the electron gun in order to reduce the input capacitance to enable the high frequency signal to be impressed on the control grid for high frequency operation.
U.S. Pat. No. 2,458,962 discloses a grid assembly for cathode ray tubes which comprises first and second grid members in the form of a frustum of a cone. The first grid member is closely positioned next to the cathode and the second grid member has an inner section disposed within the first grid member but spaced therefrom. This arrangement presents a large area thereby increasing the capacitance and is not suitable for high frequency cathode ray tubes.
The grid assembly in U.S. Pat. No. 2,540,621 is of similar construction to that of U.S. Pat. No. 2,458,962 except that the first grid member does not have a frustrum of a cone configuration; however, the metal areas of the first and second grid members opposite each other present a large area such that increased capacitance results thereby rendering this grid assembly unsuitable for high frequency operation.
The grid assembly in U.S. Pat. No. 2,443,916 includes a small first grid member which is welded to an eyelet that secures the first grid member to a ceramic mounting member onto which the second grid member is also mounted and spaced from the first grid members. This arrangement provides a large surface area that results in a large input capacitance which is a serious disadvantage to high frequency operation.